Trump says "we had hundreds of new sanctions ready to go".
Asked about Pyongyang's commitment to denuclearization, Trump said: "I think they want to do that".
The United States previously blacklisted Kim Yong Chol, who once served as a bodyguard to the current leader's father Kim Jong Il, from coming to the United States because of his role in North Korea's military establishment. "Remember what I say, we will see what we will see", adding: "I look forward to the day I can take the sanctions off North Korea".
Kim Yong Chol was greeted at the White House by chief of staff John Kelly and then whisked into the Oval Office.
The president later said he had not even opened Kim's letter, saying, "I may be in for a big surprise, folks".
And where the administration once talked about a nuclear deal and one summit, Trump on Friday stressed that this is "a process" that will go on for some time: "I told them today, 'Take your time".
"I think that we're going to have a relationship and it will start on June 12", the president said. The official, Kim Yong Chol, posed for photos with Trump outside the Oval Office, and they talked amiably at Kim's auto before he was driven away. Trump himself had not read it as of Thursday, and the White House described the envelope as sealed. Nevertheless - after a wobble earlier this month when Trump briefly cancelled the planned summit - United States diplomats are negotiating with the North in NY and a summit planning team is in Singapore.
Seoul welcomed Trump's meeting with Kim Yong Chol at the White House. Pyongyang had referred to Trump as "dotard", a word the reclusive nation has used against him in the past.
It was after 18 years that a North Korean official met a USA president in the Oval Office. Everybody wants the United States. Kim has already had two meetings each with Chinese leader Xi Jinping, South Korean President Moon Jae-in, and Pompeo - once as Central Intelligence Agency director and then as secretary of state.
Those assurances, however, will do little to quiet skepticism about Trump's willingness to meet Kim.
Bitter rivals North and South Korea are on talking terms again, but their surprising cordiality still has moments of awkwardness, such when a senior North Korean official scolded a South Korean reporter over a question he didn't like.
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Martis expressed "We can anticipate, at best, a bumpy road to the [negotiations] while addressing the South Korean and Japanese contemporaries and also encircled the "Shangri-la dialogue" in singapore".
"This was a letter presentation that ended up being a two-hour meeting", Trump said later, emerging from the Oval Office in visibly good spirits for a 15-minute give-and-take with reporters.
The senior officials from the two sides agreed to establish a liaison office in the North Korean border town of Kaesong and hold military and Red Cross talks later this month on reducing tensions and resuming reunions of families separated by the 1950-53 Korean War.
But he said that, after what have now been two meetings with Kim Jong Un and three with Kim Yong Chol, he believes the North is at least ready to consider addressing USA demands for denuclearisation.
Washington is determined that Kim should agree to what US officials call the "complete, verifiable and irreversible" end of North Korea's nuclear weapons and intercontinental missile programs.
"June 12th, we'll be in Singapore", he said.
Russian Federation is the latest major nation to reach out to North Korea since Trump accepted Kim's proposal for a summit to defuse tensions. The U.S. also dispatched an advance team to Singapore to make logistical preparations for a summit.
Kim and Moon held their first summit at Panmunjom on April 27 and issued vague aspirations for a nuclear-free Korean Peninsula and permanent peace.
North Korea is not like Libya.
Trump's announcement that the summit is back on amounted to a plot twist in a reality-show back-and-forth over whether the summit would actually occur. Trump cancelled the June 12 summit last week, then suggested it could still happen. The prospect of negotiations could undercut Trump's efforts to pressure China and other countries into withholding economic aid from North Korea unless it gives up its nuclear weapons.